Shoppers are familiar with the machine-readable tags, such as laser-readable bar codes or Radio Frequency Identification (“RFID”) tags, attached to products in stores. These tags are read during checkout, and an accurate list of the items purchased is presented to the user, along with billing information and, sometimes, related advertising.
In addition to making customer check-out faster and more accurate, these product tags help the merchant to track his inventory. By knowing which products and how many of them leave the store, an automated system can place re-stock orders when supplies are running low or alert the merchant when a particular product is selling poorly.
In a related scenario, a merchant or wholesaler actively inventories the stock on hand by scanning the machine-readable tags in a given location (e.g., on a particular shelf in a warehouse). The read-out (from the tags) of the items actually present can be cross-referenced against a list of items presumed to be present (produced by, e.g., an inventory system that tracks products coming into and products leaving a given area). If discrepancies due to theft or due to inaccurate scanning are found, they can be corrected.
Taking inventory by scanning for machine-readable tags placed on the items has some shortcomings, however. In addition to the obvious problems of missing, duplicate, or wrongly applied tags, the nature of the scanning process itself allows for some inaccuracies. When a user initiates a scan from a hand-held scanning device, the device makes a record of all of the tags that it “sees” during the scan. But it is not always certain that the scan registers all of the tags in the location that the user intended to scan and registers none of the tags in locations that the user did not intend to scan. There are several possible reasons for this. Some scanners (e.g., RFID scanners) can identify tags at a wide angle from the direction in which the scanner is pointing when the scan is initiated. Also, the range of the scan can vary from moment to moment depending on environmental circumstances. (Radio noise can limit the effective range of radio-based scans, while dust can limit laser scans.) These and other characteristics of the scanners typically in use today mean that the user may not know exactly the scope of the scan. For example, the user may wish to inventory the products on one shelf in a warehouse. However, if the user is not very careful with positioning and pointing the scanner during the scan, the scanner may miss some of the items on the shelf or may pick up items on other, nearby, shelves.